Geology and the Skiing Experience

LEAD STORY

GEOLOGY AND THE SKIING EXPERIENCE

BY BRIAN K. JONES

There is a moment, right after sunrise, when the mountain seems to hold its breath. It’s cold alright, no more than a few degrees, but a windless cold doesn’t penetrate good gear, and ski instructors wear the best. On light snow mornings, when the ski patrol isn’t lobbing 4-pound bombs into every potential avalanche chute, we roll onto the chair lift at 8:45, a full 30 minutes before the public.

The conditions are always soft, sometimes four inches of fluff, with 8% moisture that vaporizes with each turn in the cold morning air; sometimes soft corduroy that your edges cut through in wide arcing lines; sometimes nothing more than a mist.

You can get spoiled by snow conditions like this when you’re a ski instructor. I got spoiled years ago.

Even back in my early days of high school, skiing in the Sierra Nevada Mountains, I would often stop at the side of the run and let my friends go ahead. I was fascinated by the shapes of ski areas, the U-shaped valleys, the concave slopes, aretes, cirques, headwalls, hanging valleys, the pitches and the rolls. The Cascade Mountains were always fascinating to me as well, long before I became a geologist, before plate tectonics was a household word and before I knew a two-pyroxene andesite from a tholeiitic basalt.

The author in his natural environment.

I was in love with the whole experience. So, when the price of gold collapsed in 1998, I took a break from geology and applied for a job as a ski instructor at The Canyons ski resort in Park City, Utah. A year later I joined the staff of the Alf Engen Ski School at Alta, as a full-time ski instructor, a dream I had never imagined.

The quality of the skiing and instruction was demanding at Alta. Although I was eager enough and bold enough, my skills were not well developed and it took several years of training to get me into shape. Eventually I was teaching mogul and powder lessons and arcing down the groomers with my colleagues.

To my surprise, everyone - students and staff - were interested in the geology of this alpine paradise. Starting in my first year of teaching at Alta I was encouraged by the ski school to give slide shows on the geology of the Wasatch Mountains in the evenings – always with a work sheet. People like having a work sheet. They were well attended.

The late Precambrian is well represented at Alta by the Big Cottonwood Formation, a greenschist-facies felsic metamorphic complex and the Mineral Fork Tillite, varved marine deposits with ‘drop stones’ rafted in by ice sheets. This tillite is one example of the global ‘snow-ball earth’, where about 800 million years ago, most of the earth apparently froze over.

The Paleozoic section is well represented at Alta and off-trail skiers get to know many of these rocks far too well, when they choose the wrong line. The Cambrian Tintic Quartzite is bad news for your edges off-trail and the overlying Ophir Shale is hardly any better, always making its presence known on the High Traverse. Off-trail skiers at Alta get a crashcourse in Moh’s hardness scale as they discover the beveling of their edges.

The middle and upper Paleozoic and much of the Mesozoic is represented by limestones, which are softer and easier on your edges, but these rocks tend to be cliff-formers. The pearls of the Paleozoic section are the Mississippian horn corals, beautifully preserved like miniature cornucopia in a horizon about a foot thick.

Schematic of common glacial features.

The rocks get truly interesting when a 60 m.y. old granodiorite intruded the carbonate section, marmorizing, bleaching, decalcifying and finally forming a dizzying array of skarn minerals from grossularite garnets to feathery retrograde minerals. Along with this came the lead-silver minerals that made Alta famous as a mining district in the early years before skiing. There were lenses of ore in dolomite that contained 50% lead and 50 oz/ton silver. They were rich enough to be worth a fortune and complex enough to require a long train ride to New York, and a much longer ship ride to London for smelting.

Glacial features at Mt. Conness: Glacial features of Mt. Conness (California). Blue oval defines the area of the glacial cirque.

In 1938, most of the mines were running out of ore and a make-shift chairlift was constructed. They used spare parts from the old mining trams and the chair lift broke a lot. It finally operated in 1939 and opened the door to skiing in Little Cottonwood Canyon.

All of these are stories for the evenings at a ski area in the winter, where the rocks are buried deep beneath the snow. The story that rings loudest to the skiers is the story of the glaciers. When I show slides of the shapes created by glaciers in the evening, skiers will identify these shapes the next day and feel them beneath their feet.

The Little Cottonwood Glacier, 14 miles long, 2-4 miles wide and well over 1,000’ thick, was the trunk glacier. A trunk glacier is the main, large glacier that was fueled by the large ice field near the ridgeline. Little Cottonwood Glacier roared down the canyon 16,000 years ago at a handsome clip of about 10 ft/ day. The trunk glacier blazed a trail, following the easy way down the mountain, starting in Albion Basin and ending in Lake Bonneville. Today, near its top, it is the safe home of the beginning skier, because the glacier rounded all the rough edges, providing smooth skiing from top to bottom.

Farther down canyon, tributary glaciers poured into the trunk glacier. The tributary glaciers were smaller and when they melted, they left behind steep, hanging valleys where there once had been ice falls. These are only comfortably navigable by experienced skiers.

Map of the Wasatch Mountain Ski Areas

As the Wasatch Mountains were experiencing glacial events, mountain glaciers occupied most of the higher elevations of the Rocky Mountain Cordillera. Glaciers consistently carve out the same terrain: U-shaped valleys, concave slopes, hanging valleys, aretes, headwalls and glacial moraines. Many ski areas in the Rocky Mountains share these characteristics and these features are an adventure to discover.

With surprisingly high attendance at my evening slide shows, the Alf Engen Ski School rented a small plane so that I could photograph glacial features to use as teaching tools. Photos 1 through 5 show a transect from west to east across the Wasatch Mountains.

PHOTO 1: General view looking up Little Cottonwood Canyon.

Photo 1 is a general view looking up Little Cottonwood Canyon with Snowbird in the foreground and Alta in the distance. Note the distinct U-shaped valley and concave slopes. At the far right is the steep run-out from Gadd Valley at Snowbird. Near the center is the hanging valley of Snowbird’s Peruvian Gulch.

PHOTO 2: Peruvian Gulch, Collins Gulch.

Photo 2 shows Peruvian Gulch at Snowbird on the right, Collins Gulch at Alta in the middle and Albion basin in the distance to the left. Note the post glacial creek valleys in the hanging valley at Peruvian Gulch. This makes for some tough sledding.

Collins Gulch was also occupied by a tributary glacier and the steep hanging valley is well defined. At the top of the valley is a large, well defined cirque. To the left of Collins Gulch, the long, steep, continuous run into Little Cottonwood Canyon is called Alf’s High Rustler and is the signature run at Alta because of its length and pitch. But like all well-behaved ski slopes in U-shaped glacial valleys, the lower you go, the gentler the slope becomes. It scares the living daylights out of you at the top and seems like a piece of cake at the bottom, luring you back for another try.

PHOTO 3: Albion Basin.

Photo 3 is Albion Basin at Alta. This was the home of the trunk glacier and the giant ice field that fueled it. As a result, there is no hanging valley, no steep pitches and long easy slopes that suit beginning and intermediate skiers. The cliffs in the distance are Devil’s Castle, composed of upper Paleozoic and Mesozoic carbonate rocks. This is the headwall of the trunk glacier, which is also an arete, a knife edge ridge. Albion Basin is a broad cirque, with smaller, more distinct cirque depressions within it. One of these contains a tarn, a cirque that is partially filled with water.

PHOTO 4: Brighton.

Photo 4 crosses the summit of the Wasatch Mountains to Brighton Ski Area. This was the home of the ice field and trunk glacier of neighboring Big Cottonwood Canyon. Like Albion Basin, Brighton has lots of easy terrain, as well as every combination of more challenging terrain. Brighton intentionally caters to younger local skiers and snowboarders from the Salt Lake Valley.

PHOTO 5: Deer Valley and Park City.

Photo 5 is Deer Valley. Located to the northeast on the leeward side of the mountain range, the topography is completely different from Brighton, Solitude, Alta and Snowbird. Deer Valley receives about 60% of the annual precipitation measured at Alta and Snowbird. Precipitation was also less during the most recent glaciation. The elevations are about 1,000’ less as well and the glaciers were not nearly as extensive. Deer Valley has the appearance of rolling hills, and the ski slopes are mostly convex, quite different from the concave slopes of the severely glaciated U-shaped slopes to the west. This has a huge effect on snow quality. North-facing concave slopes spend a lot of the winter in the shade, particularly near the glacial headwalls. When the sun does reach them, it’s at a low angle and causes little melting. Convex slopes are less shaded and feel the full force of the winter sun. Don’t get me wrong, Deer Valley is a wonderful ski area, but the snow quality does not compare with the other ski areas.

PHOTO 6: Moraines and Range Front Fault.

Photo 6 brings us back to the western range front of the Wasatch Mountains. Little Cottonwood Canyon is visible in the shade to the left and Bells Canyon, an adjacent glaciated valley, is on the right. A terminal moraine is perfectly preserved at the bottom of Bells Canyon. Behind it is Lower Bells Canyon Reservoir, home of a large population of healthy cutthroat trout that have provided great fishing. To the left of this is a distinct straight ridge, which is the lateral moraine of the Little Cottonwood Canyon glacier. There is no remaining terminal moraine from this glacier, because the glacier extended into Lake Bonneville and the moraine was obliterated by wave action from the lake. Lake Bonneville was formed by the glacial outwash from the melting glaciers. It occupied a closed basin that extended up into southern Idaho (150 miles), west to Wendover (120 miles) and south to near Cedar City (200 miles). It was big. The Great Salt Lake is an evaporite, a remnant of Lake Bonneville.

There is a distinct series of parallel fault scarps crossing the photograph, cutting the lateral moraine and running right through the Bells Canyon terminal moraine. Moraines are dated at 16,000-18,000 years. This is the Wasatch Fault, the primary geologic structure in the area. There is 100 to 130’ of vertical offset along some of these scarps, indicating repeated large earthquakes in the past 18,000 years. According to the Utah Geological Survey, major earthquakes (7+ magnitude) occur along the fault about every 1,000 years.

The Wasatch Fault makes it all happen. The Wasatch Fault created the mountains, that trapped the snow, that formed the glaciers, that carved out the valleys and created the ski areas. And it is the Wasatch Fault that is lifting the mountains today. This causes storms to rise and dump mountains of snow in the alpine valleys each winter.

The Wasatch Mountains are an amazing geologic feature. They are only about 20 miles across. They rise from the Salt Lake Valley at an elevation of 4,500’ to over 11,000’ over a distance of about four miles. It is a formidable barrier to the east-marching storms and marks the eastern edge of the Great Basin.

Driving up Little Cottonwood Canyon we cross through six climate zones. Beginning in the desert steppe of sagebrush and rabbit brush, we travel through the oak woodland, a brief glimpse of juniper forest, then Douglas Fir and finally Engelman Spruce and Subalpine Fir. Hop on a chair at Alta or Snowbird and you’ll ride through the limber pines up into the Krumholtz zone, the zone of stunted trees. Slap your skis over your shoulder to climb to the top of Mt. Baldy and you’ll stand in alpine tundra, all of this over a distance of about 10 miles. Skiing down you’ll ski over 800 million years of Precambrian, Paleozoic and Mesozoic stratigraphy, the granodiorite and the skarns and the silver deposits, in the valleys carved by glaciers a short 16,000 years ago.

There is something magical about skiing, the nearly effortless turns floating through soft snow, where the laws of gravity prevail and the effects of friction are minimal. The cold, clear alpine air adds to this exhilaration and the short chair rides up the mountain give you time to reflect. There is life everywhere; ermine dashing through the trees, snow shoe rabbits hopping across the snow, coyotes wandering under the chairs every night, looking for dropped Clif bars. The moose have gone to the leeward side of the mountains for the winter, scrounging for limbs in the shallow snow, but they’ll be back soon. Birds are everywhere; the mournful call of the black capped chickadee, the rummaging through the snow of the Clark’s nutcracker searching for seeds and the long rhythmic call of the Northern Flicker. In spring we spot a pair of mountain bluebirds darting through the trees. When you listen closely you hear the constant rustling of life.

I love to ski, but it is much more to me than round turns in the soft snow. It is a daily celebration of the mountains, the rocks, the trees and the glaciers, the history and the thriving community of critters that live in this alpine paradise.

There is a moment right after sunset when the mountain seems to hold its breath. We ski down to the locker room and share stories about the day’s adventures. Then we organize ourselves into carpools and drive down the road. But the mountain is still there and all of the things that make it so magical are still there. And they’ll be there tomorrow and the day after.

REFERENCES

Calkins, F. C., and Butler, B. S., 1943, Geology and ore deposits of the Cottonwood-American Fork area, Utah: U. S. Geological Survey Professional Paper 201, 152 pages.

Case, William F., Eldredge, Sandra N., Milligan, Mark R., and Wilkerson, Christine, undated, Geologic guide to the central Wasatch Front Canyons, Salt Lake County, Utah: Utah Geological Survey Public Information Series 87, 28 pages.

Eldridge, Sandra N., and others, 1996, The Wasatch Fault: Utah Geological Survey Public Information Series 40, 17p. Jones, B. K., 2010, Geology and the skiing experience in, Altahistory.org, website of the Alta Historical Society, 60 pages.

Kirschivink, Joseph, 1992, Late Proterozoic low-latitude global glaciation: The Snowball Earth in Schopf, J. W. and Klein, C. (eds), The Proterozoic Biosphere: a multidisciplinary study. Cambridge University Press, pp. 51-52.

Richmond, Gerald M., 1964, Glaciation of Little Cottonwood and Bells Canyons, Wasatch Mountains, Utah: U. S. Geological Survey Professional Paper 454-D, 41 pages.

ABOUT THE AUTHOR

BRIAN K. JONES is a consulting economic geologist, retired Alta ski instructor and writer. He has published numerous geologic articles, largely on metal zoning in porphyry copper systems, as well as over twenty articles on fly-fishing. He has also written three novels that he refers to as geo-thrillers, in which the hero is a geologist. He is currently on the Board of Directors of the Alta Historical Society. He lives at the base of the Wasatch Mountains with his wife Barbara. He continues to give slide shows and workshops at Alta in the evenings. Always with a worksheet.